Self-centering, anti-seizing acetabular liner

ABSTRACT

A liner adapted for insertion into an acetabular shell for use in hip arthroplasty. The liner includes a concave inner surface adapted to engage a femoral head. The liner also includes an outer surface adapted to engage the acetabular shell and a rim that extends between the inner surface and the outer surface. The outer surface includes a locking section extending from the rim, a composite-curved section extending from the locking section at a first transition point, and a dome section extending from the composite-curved section, wherein at the first transition point, the composite-curved section is tangential to the locking section.

RELATED APPLICATIONS

This application is a divisional patent application of U.S. patentapplication Ser. No. 13/623158, filed on Sep. 20, 2012, which was anon-provisional of U.S. Patent App. No. 61/541135 of the same title andfiled on Sep. 30, 2011, each of which are herein incorporated byreference in their entireties.

TECHNICAL FIELD

The present invention relates generally to an implant for use inorthopedic surgery.

BACKGROUND OF THE INVENTION

A joint within the human body forms a juncture between two or more bonesor other skeletal parts. The ankle, hip, knee, shoulder, elbow and wristare just a few examples of the multitude of joints found within thebody. As should be apparent from the above list of examples of joints,many of the joints permit relative motion between the bones. Forexample, the motion of sliding, gliding, hinge or ball and socketmovements may be had by a joint. For example, the ankle permits a hingemovement, the knee allows for a combination of gliding and hingemovements and the shoulder and hip permit movement through a ball andsocket arrangement.

The joints in the body are stressed or can be damaged in a variety ofways. For example, the gradual wear and tear is imposed on the jointsthrough the continuous use of a joint over the years. The joints thatpermit motion have cartilage positioned between the bones providinglubrication to the motion and also absorbing some of the forces directto the joint. Over time, the normal use of a joint may wear down thecartilage and bring the moving bones in direct contact with each other.In contrast, in normal use, a trauma to a joint, such as the delivery ofa large force, from an accident for, example, an automobile accident,may cause considerable damage to the bones, the cartilage or to otherconnective tissue such as tendons or ligaments.

Arthropathy, a term referring to a disease of the joint, is another wayin which a joint may become damaged. Perhaps the best-known jointdisease is arthritis, which is generally referred to as a disease orinflammation of a joint that results in pain, swelling, stiffness,instability, and often deformity.

There are many different forms of arthritis, with osteoarthritis beingthe most common and resulting from the wear and tear of a cartilagewithin a joint. Another type of arthritis is osteonecrosis, which iscaused by the death of a part of the bone due to loss of blood supply.Other types of arthritis are caused by trauma to the joint while others,such as rheumatoid arthritis, Lupus, and psoriatic arthritis destroycartilage and are associated with the inflammation of the joint lining.

The hip joint is one of the joints that is commonly afflicted witharthropathy. The hip joint is a ball and socket joint that joins thefemur or thighbone with the pelvis. The pelvis has a semisphericalsocket called the acetabulum for receiving a ball socket head in thefemur. Both the head of the femur and the acetabulum are coated withcartilage for allowing the femur to move easily within the pelvis. Otherjoints commonly afflicted with arthropathy include the spine, knee,shoulder, carpals, metacarpals, and phalanges of the hand. Arthroplastyas opposed to arthropathy commonly refers to the making of an artificialjoint. In severe cases of arthritis or other forms of arthropathy, suchas when pain is overwhelming or when a joint has a limited range ofmobility, a partial or total replacement of the joint within anartificial joint may be justified. The procedure for replacing the jointvaries, of course, with the particular joint in question, but in generalinvolves replacing a terminal portion of an afflicted bone with aprosthetic implant and inserting a member to serve as a substitute forthe cartilage.

The prosthetic implant is formed of a rigid material that becomes bondedwith the bone and provides strength and rigidity to the joint and thecartilage substitute members chosen to provide lubrication to the jointand to absorb some of the compressive forces. Suitable material for theimplant include metals, and composite materials such as titanium, cobaltchromium, stainless steel, ceramic and suitable materials for cartilagesubstitutes include polyethylene. A cement may also be used to securethe prosthetic implant to the host bone.

A total hip replacement, for example, involves removing the ball shapedhead of the femur and inserting a stem implant into the center of thebone, which is referred to as the medullary canal, or marrow of thebone. The stem implant may be cemented into the medullary canal or mayhave a porous coated surface for allowing the bone to heal directly tothe implant. The stem implant has a neck and a ball shaped head, whichare intended to perform the same functions as a healthy femur's neck anda ball shaped head.

A cup or shell may be positioned directly into the acetabulum. The cupor shell may include a porous coating for promoting bony in-growth tosecure the shell to the acetabulum. Alternatively or in addition, theshell may include an opening or a plurality of openings for receivingbone screws to assist in the attachment of the shell to the acetabulum.The cup may be made of a metal, for example, cobalt chromium, stainlesssteel, or titanium. Alternatively, the cup may be made of a ceramic orof a polyethylene. In some embodiments, the cup directly engages thehead. In other embodiments, a liner of some sort is inserted into thecup to articulate against the head. The liner may be made of metal,ceramic, or polyethylene.

Metal and ceramic liners are often locked into the shell via a taperlock, meaning that the shell includes a taper and the liner includes acorresponding taper that fits into the taper of the shell. If properlyseated, the shell taper and the liner taper engage one another and lockthe liner into the shell. However, during insertion, the conical taperof the liner may become misaligned with the conical taper of the shell,thus preventing the intended surface-to-surface lock of the conicaltapers. This is called cross-locking, characterized by a less stableedge or multi-point lock. If a misalignment exists during insertion,there is an increased risk of implant facture and other complicationsduring surgery.

When a liner becomes cross-locked, the surgeon must decide whether toleave the liner in the cross-locked position, try to remove the linerfrom the shell, or remove the entire implant construct. Leaving across-locked liner in the shell presents multiple risks to the patientincluding: increased wear, disassembly of the implant construct,non-optimal range of motion and implant fracture. Removing the linerfrom the shell or the entire construct also creates risks and addscomplications to the surgery.

Therefore, there is a need for a liner that eliminates or greatlyreduces the occurrence of a cross-locked taper junction.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a liner isprovided that is adapted for insertion into an acetabular shell for usein hip arthroplasty. The liner includes a concave inner surface adaptedto engage a femoral head. The liner also includes an outer surfaceadapted to engage the acetabular shell and a rim that extends betweenthe inner surface and the outer surface. The outer surface includes alocking section extending from the rim, a composite-curved sectionextending from the locking section at a first transition point, and adome section extending from the composite-curved section, wherein at thefirst transition point, the composite-curved section is tangential tothe locking section.

In another embodiment, a kit for use in arthroplasty is provided. Thekit includes a shell and a liner adapted to be inserted into the shell.The liner includes an inner surface and an outer surface. The innersurface is generally concave and the outer surface is adapted to engagethe acetabular shell. The outer surface includes a locking section and acomposite-curved section, the composite-curved section including aradial portion and a straight-line tangential portion.

In yet another embodiment of the present invention, a liner is provided.The liner is for use in arthroplasty and includes an inner and an outersurface. The outer surface is adapted to engage an acetabular shell andincludes a locking section and a composite-curved section. Thecomposite-curved section extends tangentially from the locking section.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a liner according to one embodiment ofthe present invention.

FIG. 2 is a cross-sectional view of the liner of FIG. 1.

FIG. 3 is an enlarged view of a portion of the liner of FIG. 1.

FIG. 4 is a cross-sectional view of the liner of FIG. 1 super-imposedover a prior art liner.

FIG. 5 is a cross-sectional view of the liner of FIG. 1 in conjunctionwith a shell, with the liner in misalignment.

FIG. 6 is a cross-sectional view of the liner of FIG. 1 in conjunctionwith a shell, with the liner properly seated within the shell.

FIG. 7. is a perspective view of a liner according to another embodimentof the present invention.

FIG. 8 is a flow-chart depicting a method of using a liner and a shellaccording to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention and the advantages thereof are bestunderstood by referring to the following descriptions and drawings,wherein like numerals are used for like and corresponding parts of thedrawings.

Turning now to FIGS. 1 and 2, a liner 10 according to one embodiment ofthe present invention is shown. The liner 10 includes an inner surface(or bearing surface) 12. As shown, the bearing surface 12 in thisembodiment is generally concave. The bearing surface 12 is designed toarticulate with a femoral head (not shown). The liner 10 also includesan outer surface 14. The outer surface 14 is designed to fit into ashell 16 (FIGS. 5 and 6). The bearing surface 12 and outer surface 14are coupled to a rim 18 that extends between the bearing surface 12 andthe outer surface 14. In other words, the rim 18 is between the bearingsurface 12 and the outer surface 14. In this embodiment, the bearingsurface 12, outer surface 14, and rim 18 are all made of a singularpiece. In other embodiments, these pieces may be modular and lockedtogether.

Still referring to FIGS. 1 and 2, the outer surface 14 will be describedin greater detail. The outer surface 14 includes a locking section 20, acomposite-curved section 22, and a dome section 24. In this embodiment,the dome section 24 includes a flattened top portion 24 a as is commonin some prior art liner designs. However, it should be understood thatin some liners 10, there may not be a flattened top portion. The lockingsection 20 extends from the rim 18 and is sized and shaped to engage theshell 16 as will be described in more detail below. In this embodiment,the locking section 20 is a conically tapered wall, but other knownlocking mechanisms may be used.

In the embodiment illustrated in FIGS. 1 and 2, the composite-curvedsection 22 includes two portions: a radial portion 25 and a tangentialportion 26. In the illustrated embodiment, the radial portion is curvedand the tangential portion 26 is a straight line. In other embodiments,the tangential portion 26 may also be curved, having a radius that isdifferent from the radius of the radial portion. As shown in FIG. 3, anenlarged view of the liner 10 around the composite-curved section 22,the locking section 20 is tangential to the radial portion 25 at atransition point 28. In other words, the radial portion 25 extendstangentially from the locking section 20. Because the radial portion 25is tangential to the locking section 20, there are no edges and there iscontinuity between the locking section 20 and the radial portion 25. Theradial portion 25 is curved having a circular radius that is tangentialto the locking section 20, thereby defining its center.

As shown in FIG. 2, the composite-curved section 22 extends from thelocking section 20 starting at the point where the locking section 20ends. In some embodiments, there is no dome section 24, and thecomposite-curved section 22 extends all the way to the top of the liner10.

Returning now to FIG. 3, the radial portion 25 tangentially blends intothe tangential portion 26 at a transition point 30. In other words, thetangential portion 26 extends tangentially from the radial portion 25 atthe transition point 30. The radial portion 25 is tangential with thetangential portion at point 30, so that no edge or sharp point exists onthe liner 10. The tangential portion 26 is a straight line that is alsotangential with the dome section 24 at a transition point 32. In otherwords, the tangential portion 26 is a straight line that is tangentialto both the radial portion 25 and the dome section 24. By having thetangential portion 26 be tangential to both these two curved areas 24,25, there are no edges or corners, reducing rough surfaces. Thetangential portion 26 is a straight line in the embodiment illustratedin FIGS. 1-3. In other embodiments, the tangential portion 26 may becurved. In yet other embodiments, as described further in FIG. 7, theremay not be a tangential portion. The composite-curved section 22 mayonly include the radial portion 25.

Looking at FIG. 4, the liner 10 is shown super-imposed over a prior artliner (line 34). As can be seen the composite-curved portion 22 extendsoutwardly from the corresponding outer portion 34 of the prior artliner. This additional material is represented by shaded portion 35 inFIG. 4. The additional material in the liner 10 reduces the amount ofclearance between the liner 10 and the shell 16 when the two pieces areassembled as will be further illustrated in FIGS. 5 and 6 below.

In some embodiments, the curvature of the radial portion 25 isdetermined by maximizing the radius of the radial portion 25, whilestill being able to create a tangential portion 26 that is tangential toboth the radial portion 25 and the dome section 24. However, in otherembodiments, other parameters may determine the curvature of the radialportion 25.

Turning now to FIGS. 5 and 6, the liner 10 is shown inserted into ashell 16. The shell 16 includes an inner surface 36 and an outer surface38. The outer surface 38 is designed to fit in an acetabulum (notshown). The inner surface 36 includes a locking section 40 that isdesigned to mate with the locking section 20 of the liner 10. In thisembodiment, the locking section 40 is a taper that mates with thetapered locking section 20 of the liner 10. In this embodiment, thelocking sections 40, 20 of the shell 16 and liner 10 are self-lockingtapers as is known in the art.

When the liner 10 is first introduced into the shell 16, if the lockingsections 20 and 40 are misaligned as shown in FIG. 5, the liner 10“floats” within the shell 16 and is not flush within the shell 16. Inother words, the rim 18 of the liner 10 is not flush with a rim 42 ofthe shell 16. This allows the user to ensure alignment between thelocking sections 20, 40 of the liner 10 and shell 16 before seating. Asdescribed above, the composite-curved portion 22 includes added material(shaded portion 35 from FIG. 4), reducing the clearance between theliner 10 and the shell 16. Thus, unless the locking sections 20 and 40of the shell 16 and liner 10 are aligned, the composite-curved portion22 abuts the shell to keep the liner from dropping into place. Once theliner 10 and shell 16 are aligned, the locking sections 20, 40 engageand the locking section 20 of the liner 10 is in full taper contact withthe locking section 40 of the shell 16 and the liner 10 and shell 16 canbe fully seated as shown in FIG. 6. If a liner 10 is fully seated in theshell 16, the rim 18 of the liner 10 is flush with the rim 42 of theshell 16.

FIG. 7 illustrates another embodiment of the present invention. Theembodiment includes a liner 50. The liner 50 includes a locking section52, a composite-curved section 54, and a dome section 56. In thisembodiment, the composite-curved section 54 comprises a single curvedportion 58. In other words, there is not a straight-line tangentialsection as described in the embodiment of FIGS. 1-6 above. The curvedportion 58 of the composite-curved section 54 extends from a point 55where the locking section ends. In some embodiments, there is no domesection 56 and the composite-curved section 54 extends to the top of theliner 10. In other embodiments where there is a dome section 56, thecomposite-curved section 54 blends into the dome section 56 at a point59. In this embodiment, the curved portion 58 extends tangentially fromthe locking section 52 and from the dome section 56.

Turning now to FIG. 8, a method of using one embodiment of the presentinvention is described. At step s60, the shell 16 is inserted into theacetabulum (not shown). The liner 10, 50 is placed into the shell (s62).If the liner 10, 50 is floating, then the user rotates the liner 10, 50(step s64) until it slips into the shell 16 as shown in FIG. 6. In someembodiments, step s60 may be done after the liner 10, 50 is insertedinto the shell. In other words, the liner/shell combination could beeither assembled in the operating room or it could come pre-assembled asin a monoblock shell with having the liner and shell assembled togetherbeforehand. The user may be the surgeon assembling the shell and linerduring the surgery, or the user could be someone who preassembles thedevice and then the shell and liner assembly is delivered to the surgerypreassembled.

While the invention is susceptible to various modifications andalternative forms, a specific embodiment thereof has been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit theinvention to the particular form disclosed, but on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theappended claims.

1. A liner adapted for insertion into an acetabular shell for use in hiparthroplasty, the liner comprising: a concave inner surface adapted toengage a femoral head; an outer surface adapted to engage the acetabularshell; and a rim extending between the inner surface and the outersurface, wherein the outer surface includes a locking section extendingfrom the rim, a composite-curved section extending from the lockingsection at a first transition point, and a dome section extending fromthe composite- curved section, wherein at the first transition point,the composite-curved section is tangential to the locking section. 2.The liner of claim 1, wherein the composite-curved section includes aradial portion and a tangential portion.
 3. The liner of claim 2,wherein the radial portion extends from the locking section at the firsttransition point.
 4. The liner of claim 2, wherein the tangentialportion is a straight line.
 5. The liner of claim 4, wherein thetangential portion extends from the radial portion at a secondtransition point.
 6. The liner of claim 5, wherein the tangentialportion is tangential to the radial portion at the second transitionpoint.
 7. The liner of claim 2, wherein the dome section extends fromthe tangential portion at a third transition point.
 8. The liner ofclaim 7, wherein the tangential portion is tangential to the domesection at the third transition point.
 9. The liner of claim 1, whereinthe dome section extends from the composite-curved section at atransition point and the composite-curved section is tangential to thedome section at the transition point.
 10. The kit of claim 10, whereinthe composite-curved section extends tangentially from the lockingsection.
 11. The kit of claim 10, wherein the liner further includes adome section that extends tangentially from the composite-curvedsection.
 12. The kit of claim 14, wherein the dome section includes aflattened top portion.
 13. A liner for use in arthroplasty, the linercomprising an inner surface and an outer surface, the inner surfacebeing generally concave, the outer surface adapted to engage anacetabular shell, the outer surface including a locking section and acomposite-curved section, wherein the composite-curved section extendstangentially from the locking section.
 14. The liner of claim 16,wherein the outer surface further includes a dome section, the domesection extending tangentially from the composite-curved section. 15.The liner of claim 17, wherein the composite-curved section includes aradial portion and the dome section extends tangentially from the radialportion.
 16. The liner of claim 16, wherein the composite-curved sectionincludes a radial portion having a radius and a tangential portion. 17.The liner of claim 16 further comprising a rim between the inner andouter surfaces.